High voltage discharge apparatus



April 24, 1934. F, R, ELQER 1,956,416

` HIGH Yonne: insomma APPAMWS Filed Mign 28., 1.930v

inventor" FrfamK R. E kier,

MM MW His A'CCoreg.

Patented Apr. 24, 1934 OFFICE HIGH VOLTAGE DISCHARGE APPARATUS Frank B. Elder, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application August 28, 1930, Serial No. 478,421

' 2 Claims.

My invention relates to high voltage discharge apparatus, particularly to controlling means for apparatus used in connection with X-ray or cathode ray tubes, and has for its principal object the provision of an improved switch means for controlling the discharge of electric condensers forming part of such apparatus.

In the use of switch devices for controlling the discharge of condensers associated with the induction coils of X-ray or similar apparatus diiliculties have been encountered heretofore due to various causes among which is the loss of energy in the spark occurring when contact is made at `the condenser switch. n

AnY instance of such difculty is met with when the condenser forms part of apparatus for breakingr the primary circuit of an X-ray induction coil. In the operation of such coils it is necessary that means be provided to cause a quick break of the primary circuit of the coil. It has been suggested heretofore to utilize for this purpose an arc discharge device comprising an anode and a mercury cathode by connecting this device in circuit with the coil primary and a current source and sub- 2' sequently interrupting the current llow between the anode and cathode of the device. To accomplish the interruption of this current ow, switch means are provided whereby a charged condenser is arranged to be connected in circuit with the anode and cathode of the mercury arc device. 'I'he polarity of the condenser terminals with respect to those of the mercury arc discharge device is such that, when the condenser is connected thereto, potentials are impressed on the anode and cathode of the device which cause the extinction of the cathode spot on the mercury cathode, and consequently the substantially instantaneous interruption of the current in the circuit including the discharge device and the coil primary.

It has 'been found that when the above described condenser is charged only to a low voltage an ordinary mechanical switch is satisfactory for the purpose of closing the circuit including the condenser vand the electrodes of the mercury arc device, but when the arc to be extinguished in this device is large, the capacity of the low voltage condenser must also be large, and, while the cathode spot may be extinguished when the switch is closed to discharge this condenser, nevertheless the rise of voltage in the primary of the induction coil at break of the primary circuit is small, because the desired rise of voltage is prevented by the large capacity condenser, which is caused to be connected to the coil pri- (Cl. Z50-34) mary when the condenser switch is closed. It is necessary, therefore, when the arc to be extinguished in the mercury arc device is large, to use a condenser having a. small rather than a large value of capacity. But when the capacity is made small the voltage to which the condenser is charged in order to extinguish the arc must be increased, to the order, for example, of several thousand volts. When the condenser voltage is of this order,.however, ordinary switching means such as the usual mechanical switch are unsatisfactory since a large part of the energy of the condenser charge is lost in the spark formed at the switch contacts when the switch is closed to discharge the condenser.

Difliculties have been encountered also n the use of mechanical switch means associated with X-ray or cathode ray apparatus wherein the voltage rise in the primary of an induction coil is not due to the breaking of a .circuit including the primary and a current source as above described but is due to the discharge, through the primary, of a condenser which is arranged to be charged from a suitable current source and subsequently to be connected directly to the primary terminals by the switch means.

In accordance with the present invention these dimculties are avoided by the provision of switch means for controlling the discharge of the condenser associated with the induction coil, comprising a vapor electric or arc discharge device connected in circuit with the condenser and having an anode, a cathode and a, control electrode; the switch means further comprising means, controllable manually or otherwise, for impressing a potential on the control electrode to permit the condenser discharge current to flow between the anode and cathode.

My invention will be better understood from the following description when considered in connection with the accompanying drawing and its scope will be pointed out in the appended claims:

Referring to the drawing, Fig. 1 is a diagrammatic view of apparatus in which my invention is embodied and Figs. 2 and 3 are.diagrammatic 100 views of modifications of the invention.

In the embodiment of the invention illustrated in Fig. 1 an inductance device 10, such as an induction coil, is shown comprising a primary winding 11 connected to a source of current 12 and a 105 secondary winding 13 connected to a circuit 14 which mayinclude high voltage discharge apparatus such as an X-ray tube (not shown). In order to provide means for breaking the current in the circuit including the primary 11, an arc discharge device 15 comprising an anode 16 and a mercury cathode 17 is *.onnected in series with the primary 11 and current source 12, and a condenser 18 which is charged by any suitable means, as from an alternating current source 19 through a rectifying device 2O having a cathode 21 and an anode 22, is arranged to be connected while in charged condition in shunt to the anode and cathode of the mercury device by a switch means 23. Tn accordance with my invention this switch means comprises a vapor electric or arc discharge device 24 having an anode 25, a cathode 26 and a control electrode 27, and further comprises means to impress potentials on the electrode 27 to control the flow or current between the anode 25 and cathode 26. For this latter purpose there may be provided a transformer device 28 having one winding 29 connected to the control electrode 27 and cathode 26 and another winding 3i) arranged to be connected in series with a current source 31 by a contact device such as a key 32.

The arc discharge device 24 is preferably of the type in which current cannot flow between anode 25 and cathode 26 until a potential positive with respect to the cathode is impressed on the control electrode 27. Since in the present embodiment of the invention the control electrode is maintained normally at the potential of the cathode by reason of its connection thereto through winding 29, current from condenser 13 cannot normally flow in arc discharge device 24. To permit the initiation of this current ow, windings 29 and 30 and source 31 are so arranged that, upon closing of key 82, a potential which is positive with respect 'to cathode 26 is impressed on control electrode 27. t will be understood that other arc discharge devices may also be used, oi the type, for example, in which a potential negativtv with respect to the cathode is required to be imi` essed on the control electrode, to prevent flow of current between anode and cathode. In this case it will be obvious that any suitable means for providing the negative control electrode bias potential may be used such as a current source connected in the circuit between the cathode and the control electrode.

In the operation o the system illustrated in Fig. 1 current supplied by source 12 in the circuit of the induction coil primary 11 flows between anode 16 and mercury cathode 17 of the arc discharge device 15. To eiect a quick break of the primary current and thereby to produce an efiicient discharge in high voltage apparatus which may be comprised in circuit, from the secondary 13 of the induction coil 10, the cathode spot on mercury cathode 17 is arranged to be extinguished by the discharge of condenser 18, previously charged from the alternating current source 19 through rectifier 20. The discharge of the condenser is accomplished in accordance with the invention by the switch means 23. Operation of this switch means except at the time the condenser is to be discharged is prevented by the arc discharge device 24, since no current normally flows between anode 25 and cathode 26 of this device. When it is desired to discharge the condenser 18 a potential is impressed on control electrode 27. by operation of the key 32 controlling the potential source 31, of such value that current may ow between the anode and cathode of the device 24. which then operates as a closing switch between the condenser and the mercury arc device 15.

The switch means above described, utilizing the potential controlled arc discharge device V24: as a,

condenser switch in place of the usual mechanical switch, has been found to function eillciently and without the loss of energy due to formation of a spark when the condenser circuit is closed. For example, using a mercury arc tube 15 rated at 50 amperes, it has been found possible bythe use of the arc discharge device 24 as a closing switch for the condenser 18, to break successfully a current of 55 amperes in the circuit of induction coil primary 11, the condenser 18 being or approximately 0.1 mf. capacity and charged to 12000- 15000 volts.

In the modification of the invention shown in Fig. 2 the primary 11 of induction coil 10 is arranged to be connected directly to a condenser 18 which is charged through a rectiiier 20 from an alternating current source 19 in the same manner as above described in connection with Fig. l. The switch means 23 comprising arc discharge device 24, transformer device 28, current source 31 and key 32, is provided to close the circuit including the condenser 18 and the primary 11.

In the operation of the system shown in Fig. 2, the discharge in circuit 14 from secondary 13 of the transformer 10 is not produced at the break of the current flowing in primary 11 and supplied from a current source such as source 12 of Fig. 1, but is produced when the circuit including the primary 1l and charged condenser 18 is closed. This circuit is maintained normally open by arc discharge device 24 and the circuit is closed to discharge the condenser, in the same manner as described in connection with Fig. 1, by impressing a potential on control electrode 27 to permit current to iiow between anode 25 and cathode 26;

In the modification of the invention shown in Fig. 3 a plurality of units each comprising an induction coil 10, a condenser 18 and charging means therefor, and an arc discharge device 24, all as previously described in connection with Fig. 2, are arranged in cascade, the secondaries 13 of the several coils being in series with circuit 14. The means for impressing a potential on the control electrodes 27 of the devices 24 comprises a current source 31, a key 32 and a transformer de- 1V vice 33 having a single primary 34 and a plurality of secondaries 35 each connected to the control electrode and cathode of a diierent one of the devices 24. The operation of the system shown in Fig. 3 is in general similar to that of the systern of Fig. 2. In order, however, to discharge the condensers 18 simultaneously in the system of Fig. 3, the potential impressed on the control electrodes 27 is supplied from the inductance device 33 having separate secondaries for these con' trol electrodes but only a single primary 34 in which the current impulse is controlled by the single contact device, key 32.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a high voltage discharge system, an inductance device having a plurality of primary windings, a plurality of condensers, means to charge said condensers, and means to discharge each of said condensers through a dilerent one of said windings comprising a plurality of arc discharge devices each in series with a different one of said condensers and windings and each comprising an anode, a cathode and a control elec- I trode, said discharge means further comprising means to impress a potential on all of said control electrodes simultaneously to permit the ow of current between the anode and cathode of each of said discharge devices.

2. In a high voltage discharge system, an lna cathode and a control element, said discharge means further comprising means to affect all of said control elements simultaneously to permit the iiow of current between the anode and cathode of each 'ct said discharge devices.

FRANK R. mmm. 

